<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
</head>
<body>

<p id="demo">单击按钮显示文档的节点名称</p>
<button onclick="myFunction()">点我</button>
<script>
    function myFunction(){
        let x=document.getElementById("demo");
        x.innerHTML=document.documentElement.nodeName;
        console.log(document.documentElement);
    }
</script>

</body>
</html>